Preheat Oven to 350 degrees F. 1.,In a small dish, combine the salt, garlic salt, black pepper and cayenne pepper.,2.,Line the bottom of a roasting pan with the sliced onions and garlic cloves.,3.,Place the chicken halves skin side up on the onions.,Rub each half with 1 Tablespoon mustard and then sprinkle with the dry seasoning.,4.,Tightly cover with aluminum foil, making sure to seal the edges in order to capture the steam.,5.,Cook for 1 hour 15 minutes.,6.,Carefully remove the foil and spread each chicken half with BBQ sauce.,I like a Texas or Chipotle style, but use your favorite.,7.,Return the chicken to the oven for an additional 20 minutes.,8.,Using a sharp knife, carefully cut between the breast and thigh joint to separate the upper and lower quarters.,9.,______